Plasma and muscle amino acid and ammonia responses during prolonged exercise in humans

Abstract

Plasma and muscle amino acid (AA) and ammonia (NH3) responses were measured during prolonged submaximal exercise in humans. Increased NH3 production during submaximal exercise has been attributed to the activity of the purine nucleotide cycle, without consideration of any possible contribution from AA. Six men cycled at 75% of maximal O2 uptake until exhaustion on two occasions after 2.5 days of ingestion of a high-carbohydrate or mixed diet. Plasma samples (antecubital vein) and muscle biopsies (vastus lateralis) were obtained at rest and during exercise and analyzed for plasma and muscle NH3 and AA as well as muscle metabolites. There were no significant diet effects in these parameters, so the majority of results focus on the effects of exercise. Plasma and muscle NH3 increased significantly from the onset and continued to increase throughout exercise. The total and total essential [AA] of muscle were significantly increased at exhaustion, whereas both the plasma and muscle branched-chain AA contents were unchanged. This suggests that protein catabolism was occurring during exercise and the branched-chain AA were used for energy and NH3 production.

Exercise-induced changes in amino acid levels in skeletal muscle and plasma

“…It is also known that oxidation of leucine is elevated during exercise 16) . However, a cycle ergometer exercise to fatigue with a load of 75% V ・ O2max did not alter muscle BCAA levels 39) .…”

“…On the other hand, alanine levels increased during exercise, but reverted slightly in response to fatigue 38) . MacLean et al 39) also showed a gradual increase in muscle glutamate levels under a similar workload, and significant increases in alanine levels 45 min after the start of the exercise. Elevated alanine levels reverted to a certain extent at exhaustion (103 ± 8 min).…”

“…Henriksson 11) reported that a 3.5-h cycle ergometer exercise with a load of 50% V ・ O2max increased muscle levels of 3-MH, tyrosine, and phenylalanine by approximately 25%. In addition, MacLean et al 39) showed that a cycle ergometer exercise to fatigue with a load of 75% V ・ O2max increased muscle tyrosine levels. Similarly, Blomstrand and Newsholme 41) demonstrated increases in muscle tyrosine and phenyl-305 JPFSM : Amino acids in skeletal muscle and plasma alanine levels after a 30-km run and a full marathon, as well as increases in plasma tyrosine and phenylalanine levels after a full marathon.…”

The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exercise

“…Substantial ammonia and inosinic acid are produced by the deamination of adenosine monophosphate in the skeletal muscle during high-intensity exercise (Stathis et al, 1994). Moreover, the muscle's capacity to produce ATP via oxidative phosphorylation decreases during this process, and muscle fatigue occurs (Sahlin et al, 1990;MacLean et al, 1991). Inhibited homeostasis produced by this ammonia production is recovered by ammonia metabolism in the urea cycle Figure 1 Plasma ornithine, ammonia, urea, lactic acid and glutamate concentrations at times before ingestion, 1 h after ingestion, just after exhaustion and 15 min after exhaustion in both conditions.…”

“…In particular, because the ammonia production consumes substantial amounts of inosinic acid (Stathis et al, 1994), the ability to produce adenosine triphosphate (ATP) via oxidative phosphorylation in the skeletal muscles decreases. Ultimately, the accumulation of ammonia in skeletal muscle induces muscle fatigue (Sahlin et al, 1990;MacLean et al, 1991) and is linked to a decrease in performance.…”